Applied Catalysis B, Environmental (v.213, #C)
Editorial Board (IFC).
Utilization of MoS2 and graphene to enhance the photocatalytic activity of Cu2O for oxidative C―C bond formation by Zhen Li; Yuxi Pi; Danyun Xu; Yang Li; Wenchao Peng; Guoliang Zhang; Fengbao Zhang; Xiaobin Fan (1-8).
Display OmittedVisible light driven photoredox catalysis has considered as a sustainable and promising strategy for organic synthesis. Here we report a new composite material consisting of cuprous oxide (Cu2O) nanoparticles grown on layered molybdenum disulfide (MoS2) and graphene hybrids as a high-performance photocatalyst for C―C bond formation reaction. This composite material shows superior stability and reusability. The enhanced photocatalytic activity of the novel catalyst is attributed to the synergetic effects of MoS2 and graphene as cocatalysts in the composite, in which graphene serves as an excellent electron transporter, and MoS2 nanosheets provide a source of active sites. This work would open a promising way to design and fabricate the efficient composite photocatalysts for organic synthesis.
Keywords: Photocatalyst; Graphene; MoS2; Cu2O; Organic synthesis;
A C3N4 surface passivated highly photoactive Au-TiO2 tubular nanostructure for the efficient H2 production from water under sunlight irradiation by Rayees Ahmad Rather; Satnam Singh; Bonamali Pal (9-17).
Display OmittedIn context to the recent advances in the development of sunlight active nanocomposites for the renewable H2 production from water, a C3N4 passivated Au-TiO2 tubular nanocomposite (CTA) has been prepared by a facile one pot hydrothermal method. Structural and morphological studies revealed the elongated anatase TiO2 nanotubes (200–250 nm long, d = 12 nm) embedded in a thin layer of graphitic C3N4 (1–3 nm) and dispersed Au (7–12 nm) nanoparticles. The bulk C3N4 turned into monolayer due to the self exfoliation process confirmed by Raman (G band = 1545 cm−1). The potential voltage (I–V) characteristics revealed the non ohmic properties of the heterojunction with a good current response (1.385 × 10−4 A). The nanocomposite showed efficient photocatalytic activity with the production of ∼88 μmolh−1 (calculated = 2933 μmolh−1g−1) of H2 gas under direct sunlight irradiation using methanol as hole scavenger. The C3N4 is activated under sunlight and simultaneously sensitized by Au due to its plasmonic effect. The band potential of C3N4 (-1.21 eV vs NHE for ECB) is more negative than TiO2 (ECB = −0.29 Vs NHE) enabling photo induced electrons to easily pass the interface into the ECB of TiO2 which promotes the charge carrier separation and enhance the photocatalytic activity for H2 production.
Keywords: One pot hydrothermal synthesis; C3N4 passivated Au-TiO2 tubular nanostructure; Self exfoliation of C3N4; H2 production under direct sunlight; Photochemical and thermal stability;
Hydrothermal synthesis of novel heterostructured Fe2O3/Bi2S3 nanorods with enhanced photocatalytic activity under visible light by Ahmed Helal; Farid A. Harraz; Adel A. Ismail; Tarek M. Sami; I.A. Ibrahim (18-27).
Display OmittedThe development of efficient visible-light photocatalyst heterostructures remains a major concern for obtaining desirable material properties and effective carrier transformation. Here, we demonstrate, for the first time, the synthesis of novel heterostructures of Fe2O3/Bi2S3 nanorods via a one-step hydrothermal route and employed effectively as visible-light-driven photocatalysts for the degradation of organic pollutants of methylene blue dye (MB) and phenol. TEM and FE-SEM images displayed that Fe2O3/Bi2S3 heterostructure is nanorods with ∼30–60 nm diameter and 0.5–1 μm length. The newly prepared Fe2O3/Bi2S3 nanorods exhibit greatly enhanced photocatalytic activity toward both MB and phenol compared to pure Bi2S3 and the heterostructure with low molar ratio of 0.06 Fe2O3/Bi2S3 exhibits the best photocatalytic activity under visible light irradiation. A maximum degradation efficiency of MB and phenol ∼90% and 96% was accomplished using Fe2O3/Bi2S3 nanorods compared to only 60% and 69% using pure Bi2S3, respectively. The photodegradation rates for MB and phenol are promoted respectively as ∼2.6 and 3 times using Fe2O3/Bi2S3 heterostructure higher than pure Bi2S3. Photoluminescence spectra measurement along with the calculation of relative band alignment indicated that Fe2O3/Bi2S3 heterostructure significantly suppress the recombination of photogenerated charge carriers, which is beneficial to improve the photocatalytic activity. The facile synthesis approach, unique photocatalytic activity and excellent reusability of the current Fe2O3 modified Bi2S3 nanostructure make it a promising photocatalyst for the environmental remediation related fields.
Keywords: Fe2O3/Bi2S3 nanorods; Hydrothermal; Photocatalyst; Methylene blue; Phenol;
NiMo catalysts supported on Mn-Al2O3 for dibenzothiophene hydrodesulfurization application by A. López-Benítez; G. Berhault; A. Guevara-Lara (28-41).
Display OmittedModification of the traditional Al2O3 support through addition of manganese to Al2O3 mixed Mn-Al oxides was herein envisaged to obtain highly active NiMo catalysts for hydrodesulfurization application. The effect of adding manganese was determined considering different Mn-Al2O3 supports synthetized using a sol–gel approach. The manganese-containing supports were furthermore impregnated with Ni(NO3)2 + (NH4)6Mo7O24 aqueous solutions at pH = 9 and characterized at their oxide state using UV–vis diffuse reflectance and Raman spectroscopies after drying and calcination steps. NiMo/Mn-Al2O3 catalysts were also characterized at the sulfide state mainly by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Finally, the sulfide catalysts were evaluated in the hydrodesulfurization of dibenzothiophene.Results show that the oxidation state of manganese species directly influences the nature of the Mo oxide species and their interaction with the Al2O3 support. At low Mn content (up to 0.5 mol% Mn as MnO), Mn2+ species leads to weaker interaction with the support and a higher intrinsic activity of the NiMoS species. However, these promoted sites are also formed in a lower amount than without adding Mn to the support. At too high manganese content (≥2 mol% Mn as MnO), Mn3+ species are formed and react with Ni to form a spinel phase decreasing the proportion of promoted phase to be formed after sulfidation. The highest activity is therefore observed at an intermediate Mn content of 1 mol% for which a higher intrinsic activity resulting from weaker support interaction and higher sulfidation rate combine together to achieve highly active NiMo HDS catalysts.
Keywords: MnO-Al2O3 support; Mixed oxides; Sol–gel; Hydrodesulfurization;
Microwave-assisted etherification of glycerol with tert-butyl alcohol over amorphous organosilica-aluminum phosphates by R. Estevez; S. Lopez-Pedrajas; D. Luna; F.M. Bautista (42-52).
Display OmittedThe synthesis of organosilica-aluminum phosphates by a simple and cheap sol-gel method was carried out with varying amounts of two different silica precursors, 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (C) and (3-mercaptopropyl)trimethoxysilane (MPTMS); and several Al/P molar ratios. The solids were calcined in air, at different temperatures. The etherification of glycerol with tert-butyl alcohol was carried out in the liquid-phase under microwave irradiation and also by conventional heating. The incorporation of organosilica in the final solids took place in a 50–60%, as verified by TGA, ICP-MS, XPS and 1H–29Si CP MAS NMR. The highest yield to h-GTBE (21%) was obtained at autogenous pressure, 85 °C and 15 min of reaction time under microwave, on the solid prepared with 10 mmol of C; Al/P = 1.5 and calcined at 250 °C. This material, with a balanced percentage of mesopores and macropores, also exhibited the highest number of acid sites determined by acid-base titration, as well as by results from TGA and by elemental analysis. The acidity and the hydrophilic character of the solids have been found to be key parameters for the catalytic activity, whereas porosity seems to be advantageous for the reusability of the solids, avoiding deactivation.
Keywords: Amorphous organosilica-aluminum phosphate; Microwave; Etherification; Glycerol; Tert-butyl alcohol;
Study of synergetic effect, catalytic poisoning and regeneration using dielectric barrier discharge and photocatalysis in a continuous reactor: Abatement of pollutants in air mixture system by Wala Abou Saoud; Aymen Amine Assadi; Monia Guiza; Abdelkrim Bouzaza; Wael Aboussaoud; Abdelmottaleb Ouederni; Isabelle Soutrel; Dominique Wolbert; Sami Rtimi (53-61).
Photograph of plasma DBD generated on catalytic surface in planar reactor.Display OmittedIn the present work the abatement of butyraldehyde (BUTY), dimethyl disulfide (DMDS) and their mixtures in gas phase was studied in continuous reactor at three different configurations: photocatalysis (TiO2 + UV), dielectric barrier discharge (DBD) plasma and their association in the same system (DBD+ TiO2 + UV). The effect of some operating parameters such as inlet concentration of pollutant and flowrate on planar reactor performance in term of (i) BUTY removal (ii) selectivity of CO and CO2, selectivity of byproducts has been also investigated. Moreover, ozone formation has been studied to evaluate the performance of the combined process. A synergetic effect was observed by combining (DBD) plasma and photocatalysis on BUTY removal but has not been present when it was in air mixture with dimethyl disulfide (DMDS) due to the poisoning of the catalyst. Additionally, degradation was observed as a consequence of by-products accumulation on the surface of the catalyst. Moreover, the regeneration/recovery of the initial photocatalytic activity was explored in details. A significant regeneration has been occurred by combining photocatalysis and nonthermal plasma. This trend of nonthermal plasma on catalytic surface can explain the synergetic effect during the pollutant degradation time. Moreover, the catalyst was concomitant with the time required for the hydrophobic to hydrophilic transition on the catalyst surface as followed by contact angle measurement (CA). Redox catalysis was detected by X-ray Photoelectron Spectroscopy (XPS) showing Ti4+/Ti3+ switching during the degradation, poisoning and regeneration times.
Keywords: Sulfur compounds; Dielectric barrier discharge; Photocatalysis; Synergetic effect; Catalyst poisoning; Catalytic regeneration;
Bactericide effects of transparent polyethylene photocatalytic films coated by oxides under visible light by Sami Rtimi; John Kiwi (62-73).
Display OmittedThis review addresses catalytic/photocatalytic films under visible light inducing fast bacterial inactivation. These films present uniform, stable and adhesive surfaces able to inactivate bacteria within minutes. Uniform sputtered polyethylene-TiO2 (PE-TiO2) films absorbing mainly in the UV-region were later followed by studies on PE-FeOx and PE-FeOx-TiO2 absorbing light in the visible region. The amount of TiO2 sputtered on PE was significantly increased by RF-plasma pre-treatment due to the additional polar binding sites introduced on the PE-film. The hydrophobic to hydrophilic conversion of the PE-TiO2 films under light irradiation was observed to be concomitant with the bacterial inactivation time. The TiO2 diffuse reflectance spectra (DRS) of TiO2-PE-films were extensively modified by the sputtering of FeOx. The structure of the sputtered layers revealed a random deposition of FeOx-TiO2 on PE. The oxidative radical species generated on semiconductor surfaces were identified by appropriate scavenging experiments. By photoelectron spectroscopy (XPS), the redox processes occurring on the photocatalysts were evaluated. Repetitive bactericide cycling was possible for the three films discussed in this review. Bacterial inactivation mechanisms were suggested for the different films presented in this review.
Keywords: Photocatalysis; Thin films; Bacterial inactivation kinetics; Surface characterization; Sputtering; Innovative oxides;
Aligned α-FeOOH nanorods anchored on a graphene oxide-carbon nanotubes aerogel can serve as an effective Fenton-like oxidation catalyst by Yuyang Liu; Xuemin Liu; Yaping Zhao; Dionysios D. Dionysiou (74-86).
α-FeOOH@GCA greatly enhanced the discoloration of Orange II in photo Fenton-like system by promoting mass transfer and facilitating redox recycling of iron species on the surface of catalyst.Display OmittedThe self-assembled synthesis of a hierarchical graphene oxide (GO)-carbon nanotubes (CNTs)-α-FeOOH decorated composite aerogel (α-FeOOH@GCA) through a facile in-situ hydrolysis route is reported for the first time and the materials was tested for its performance as Fenton-like catalyst. The introduction of GO-CNTs clearly mediated the morphology to aligned α-FeOOH nanorods (ca. 100 nm) within aerogel matrix comparing with pristine urchin-like α-FeOOH three-dimensional microstructures (ca. 1 μm). This three dimensional porous aerogel network provided efficient charge/mass-transfer leading to great enhancement of the catalytic activity of α-FeOOH. The outstanding catalytic performance of this composite in degradation of organics with different charge and structure, i.e. Orange II (OII), rhodamine B (RhB), methylene blue (MB), phenol and endocrine disruptor bisphenol A (BPA) was demonstrated. For example, the discoloration of OII with pseudo first-order rate constant of 0.10 min−1 significantly exceeded that of pristine α-FeOOH. At relatively low concentration of α-FeOOH@GCA catalyst (125 mg L−1) and H2O2 (0.55 mM) showed excellent catalytic activity for efficient (∼99%) discoloration of OII (40 mg L−1) under a 60 min UV365 irradiation in the pH range 3–10. The different charge of five target contaminats greatly determined the surface-catalyzed degradation kinetics at natural solution pH in the order of cationic > neutral > anionic organics due to the negatively charged carbon-based aerogel matrix. The new identified desulfonation intermediates elucidated through UPLC–MS analysis indicated two reaction pathways: 1) hydroxylation and 2) desulfonation by-products followed by cleavage of the azo bond as the predominant degradation pathway of OII. The elimination of the acute toxicity of the parent contaminant to luminescent bacterium Q67 was consistent with the formation of less toxic degradation by-products identified. Free radical quenching studies accessed the role of hydroxyl radical (•OH), superoxide anion radical (O2 • −) and singlet oxygen (1O2) as the dominating reactive oxygen species (ROS). The quantitative studies to measure radical concentrations using relative molecular probes showed the effective activation of H2O2 led to high rate production of ROS accounted for OII degradation. The greatly enhanced photocatalytic property of this hybrid was correlated with the efficient conversion between Fe2+/Fe3+ and synergistic coupling between α-FeOOH and carbon-based aerogel matrix evidenced through the formation of Fe―O―C chemical bonds was verified by X-ray photoelectron (XPS) analysis. Based on its simple and scalable preparation route as well as its excellent UV365 or visible light-responsive catalytic performance, this hybrid exhibits a high potential to be used as an efficient and environmental-friendly catalyst for water remediation.
Keywords: Carbon-based aerogel; Goethite nanorods; photo-Fenton reaction; Refractory organics; Self-assembly; Textile wastewater;
Enhanced photocatalytic mechanism of the Nd-Er co-doped tetragonal BiVO4 photocatalysts by Ting Liu; Guoqiang Tan; Chengcheng Zhao; Chi Xu; Yuning Su; Ying Wang; Huijun Ren; Ao Xia; Dan Shao; Shemin Yan (87-96).
Display OmittedThe Nd/Er co-doped tetragonal BiVO4 photocatalysts are synthesized by a microwave hydrothermal method, and the crystal structures, morphologies and optical properties are characterized. The substitution of Nd3+ and Er3+ for Bi3+ sites leads to distortion of the [VO4] tetrahedron chains and induces the monoclinic structure transforming into the tetragonal structure, with the morphology evolving from nano particle agglomerations to disorganized regular rods agglomerations. The impurity energy levels induced by Nd3+ and Er3+ in the energy band of BiVO4 act as electron traps and have further energy transfer in the up-conversion processes to facilitate the photocarriers’ separation. The more positive VB positions in the co-doped BiVO4 band structures can also effectively enhance oxidation capacity. Based on the above synergetic effect, the degradation rate the degradation rate of co-doped tetragonal BiVO4 photocatalyst can reach the highest 96% within 150 min under simulated sunlight and 20 min under the NIR irradiation.
Keywords: Nd-Er/BiVO4; Impurity energy level; Up-conversion; Synergetic effect;
Enhanced performance for plasma-catalytic oxidation of ethyl acetate over La1-xCexCoO3+δ catalysts by Xinbo Zhu; Shuo Zhang; Yang Yang; Chenghang Zheng; Jinsong Zhou; Xiang Gao; Xin Tu (97-105).
Display OmittedIn this work, plasma-catalytic oxidation of low concentration ethyl acetate (100 ppm) over La1-xCexCoO3+δ (x = 0, 0.05, 0.1, 0.3 and 0.5) perovskite catalysts was carried out in a coaxial dielectric barrier discharge (DBD) reactor. The effects of Ce-doping on the removal of ethyl acetate and COx (x = 1 and 2) selectivity in the plasma-catalytic oxidation process were investigated as a function of specific energy density (SED). Compared to the plasma reaction without a catalyst, the presence of the LaCoO3 catalyst in the plasma enhanced the removal of ethyl acetate and COx selectivity. The use of the Ce-doped catalysts further enhanced the performance of the plasma-catalytic oxidation process. The highest removal efficiency of ethyl acetate (100%) and COx selectivity (91.8%) were achieved in the plasma-catalytic oxidation of ethyl acetate over the La0.9Ce0.1CoO3+δ catalyst at a SED of 558 J L−1. The interactions between Ce and LaCoO3 resulted in an increased specific surface area (by 17.1%–68.6%) and a reduced crystallite size (by 13.5%–68.2%) of the Ce-doped LaCoO3 catalysts compared to pure LaCoO3, which favours the oxidation of ethyl acetate in the plasma process. Compared to the LaCoO3 catalyst, the Ce-doped perovskite catalysts showed higher content (maximum 54.9%) of surface adsorbed oxygen (Oads) and better reducibility, both of which significantly contributed to the enhanced oxidation of ethyl acetate and intermediates in the plasma-assisted surface reactions. The coupling of plasma with the Ce-doped catalysts also reduced the formation of by-products including NO2 and N2O. The possible reaction pathways involved in the plasma oxidation process have been discussed.
Keywords: Plasma-catalysis; Oxidation; Perovskite; Non-thermal plasma; Gas clean-up;
Upgrading HDS activity of MoS2 catalysts by chelating thioglycolic acid to MoOx supported on alumina by José A. Toledo-Antonio; M.A. Cortes-Jacome; J. Escobar-Aguilar; C. Angeles-Chavez; J. Navarrete-Bolaños; E. López-Salinas (106-117).
Display OmittedAlumina-supported Mo-based hydrodesulfurization catalysts (14 wt% nominal Mo loading) were modified by thioglycolic acid (TGA, TGA/Mo = 1 mol ratio), as a chelating agent containing a thiol group. To that end, two series of catalyst were prepared: the first one by using ammonium heptamolybdate as a precursor and, in the second one, in situ obtained phosphomolybdates from MoO3 digestion in diluted H3PO4. Oxidic phases were characterized by N2 physisorption, Raman and UV–vis spectroscopies, electron microscopy and XPS. As well, the corresponding sulfided phases were studied by XPS, HR-TEM-STEM techniques, and chemical composition was determined by STEM-EDX. Formation of ligand-to-metal charge transfer (LMCT) complexes between the S-bearing TGA and Mo atoms, resulted in reduced Mo5+ species, as indicated by XPS, and was correlated to electronic transitions bands in the UV–visible spectra. On the other hand, the catalysts prepared from phosphomolybdates impregnation and TGA addition resulted in two-fold amount of Mo4+ sulfided species, as indicated by XPS. TGA impregnation redissolve and disperse the MoO3 resulting in materials particles in materials with increased stacking of MoS2 slabs on which slabs length remained essentially unaltered. Highly active (as tested in liquid-phase dibenzothiophene hydrodesulfurization) Type II sites were favored mainly in sulfided TGA-modified formulations.
Keywords: Hydrodesulfurization; Molybdenum sulfide; Thioglycolic acid; Chelating agent; Type II sites;
Efficient direct formic acid fuel cell (DFAFC) anode of nano-sized palladium complex: High durability and activity origin by Gumaa A. El-Nagar; Kamal M. Dawood; Mohamed S. El-Deab; Bahgat E. Al-Andouli (118-126).
Display OmittedThe low stability of Pd-based catalysts extremely obstructs their applied application in the direct formic acid fuel cells (DFAFCs). Herein, a novel nano-sized palladium-complex (nano-Pd complex ) with outstanding performance (activity and durability) for DFAFCs anodic reaction (Formic acid oxidation; FAO) compared to the commercial Pd-based catalysts is introduced. Morphologically, nano-sized Pd-complex shows an intersected nano-rod like structure with an average particle size ca. 17 nm. Electrochemically, nano-Pd complex modified GC electrode (Nano-Pdcomplex/GC) has 12 times higher electrocatalytic activity, 8.0 times higher electrochemical active surface area, 3.0 times higher catalyst utilization, and ca., 16 times higher stability after 5.0 h than that of traditional Pd nanoparticles modified GC electrode (PdNPs/GC) with the same Pd loading. This significant enhancement in both activity and stability is attributed to nano-Pd complex bulky structure hindering the agglomeration of the Pd active sites and inhibiting the adsorption of poisoning CO-like intermediate species. DFT studies shows that nano-Pd complex has two different geometries: (a) cis-structure which has a square planar geometry and it is inactive for FAO, and (b) trans-structure with a tetrahedral geometry and it is highly active for FAO. This study introduces a new promising category of Pd-based catalyst with high activity, catalyst utilization and durability for DFAFCs applications.
Keywords: Fuel cells; Nano-Pd-Complex; Nanostructured; Electrocatalysis;
Preparation of g-C3N4 nanorod/InVO4 hollow sphere composite with enhanced visible-light photocatalytic activities by Zengyu You; Yuxuan Su; Yang Yu; Hui Wang; Tian Qin; Fang Zhang; Qianhong Shen; Hui Yang (127-135).
Display OmittedA novel g-C3N4 nanorod/InVO4 hollow sphere composite was fabricated through a facile template-free method. The structure-property relationship was analyzed, and the formation mechanism of such structure and morphology was also proposed based on the observation from time-dependent morphology evolvement. The results show that InVO4 hollow spheres uniformly load on the surface of g-C3N4 nanorod and thus forming the heterojunction with an intimate interface. The bulk g-C3N4 experiences a possible peeling process to form the rod-like structure, during which the mass ratio of InVO4 and ultraphonic process play a key role. Moreover, bubble-template is believed to determine the formation of InVO4 hollow sphere. Owing to this unique structure and morphology, the enhanced visible-light photocatalytic activities are achieved because of the synergistic effect of light harvesting, high transfer efficiency and enhanced separation efficiency of photo-generated carriers. And more importantly, this fabrication method combines heterojunction constructing with morphology controlling of g-C3N4 in one step, and thus may supply a new idea for the preparation of other g-C3N4 based composites.
Keywords: g-C3N4; InVO4; Nanorod; Hollow sphere; Photocatalysis;
Fabrication of hollow mesoporous SiO2-BiOCl@PANI@Pd photocatalysts to improve the photocatalytic performance under visible light by Yi Tian; Wei Li; Chenhui Zhao; Yufei Wang; Baoliang Zhang; Qiuyu Zhang (136-146).
Display OmittedA facile method was developed to synthesize a series of hollow mesoporous SiO2-BiOCl@PANI@Pd (HBPP) photocatalysts with super adsorption performance, plasmonic effect and fast interfacial charge migration. The samples were characterized by XRD, FETEM, FT-IR, XPS, DRS, etc. Photocatalytic degradation of methyl orange (MO) by HBPP composites was investigated.Results showed that the photocatalytic property of HBPP composite was superior to that of hollow mesoporous SiO2-BiOCl@PANI (HBP) composite under visible light irradiation, and the HBPP5wt% photocatalyst synthesized under 140 °C exhibits the highest photocatalytic activity. In this photocatalysis system, the orderly mesoporous opening structure of the hollow mesoporous SiO2 sphere could effectively facilitate the transfer of reactant molecules, and the existence of the internal cavities would effectively prolong the action time of the irradiated light for the multiple reflections. Moreover, the formation of interacted interfaces between the semiconductor BiOCl and conducting polymer (polyaniline) could effectively improve the separation of the photogenerated electron-hole pairs, and the palladium nanoparticles (Pd NPs) with strong localized surface plasmon resonance (LSPR) absorption band in the near-UV region could effectively induce the generation of the photoexcited electron-hole pairs in BiOCl, thus the as-obtained photocatalyst exhibits superior photocatalytic activity under visible light irradiation. The work may set foundation for application of the new photocatalyst of HBPP-based LSPR and make an important step forward remedying environmental pollution.
Keywords: Hollow mesoporous silica; Hybrid photocatalysts; LSPR; BiOCl; Polyaniline;
Metal oxide semiconductor nanomaterial for reductive debromination: Visible light degradation of polybrominated diphenyl ethers by Cu2O@Pd nanostructures by Edward B. Miller; Elsayed M. Zahran; Marc R. Knecht; Leonidas G. Bachas (147-154).
Display OmittedPolybrominated diphenyl ethers (PBDEs), which have found extensive use as flame-retarding additives to many polymer materials, are now environmentally ubiquitous and persistent pollutants that present potential health risks to humans and wildlife. Herein, we report for the first time the use of metal oxide semiconductor nanostructures for photocatalytic reductive debromination of PBDEs using visible light. Well-defined cubic Cu2O crystals, surface-decorated with Pd nanoparticles, were prepared via a hydrothermal approach. The Cu2O@Pd demonstrated light-activated tandem photocatalysis, in which Cu2O produces H2 from H2O under visible light irradiation; the evolved H2 is subsequently activated by Pd to achieve the reductive hydrodehalogenation of the PBDE. Cu2O@Pd demonstrated effective debromination of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47), one of the PBDEs of greatest environmental concern, with initial pseudo-first-order rate constant of 0.21 h−1. It is shown that the reaction proceeds via a reductive mechanism with preferential debromination at the para positions. Reaction rates for various monobromo- and dibromo-congeners were evaluated, confirming that the debromination order of preference is para > meta >> ortho, which is opposite to the order reported for direct photolysis. We conclude that Cu2O@Pd is a promising photocatalyst for reductive dehalogenation of halogenated organic compounds.
Keywords: Metal oxide semiconductor; Photocatalytic debromination; Polybrominated diphenyl ethers; PBDE; Photolysis;
Superior photocatalytic properties of carbonized PANI/TiO2 nanocomposites by Marija Radoičić; Gordana Ćirić-Marjanović; Vuk Spasojević; Phil Ahrenkiel; Miodrag Mitrić; Tatjana Novaković; Zoran Šaponjić (155-166).
Display OmittedA simple bottom–up method for the preparation of novel and very efficient photocatalytic nanocomposite system based on carbonized form of polyaniline (PANI) and colloidal TiO2 nanocrystals has been developed. The carbonized PANI/TiO2 nanocomposites were synthesized in a two-step procedure. Firstly, non-carbonized PANI/TiO2 nanocomposites were synthesized by the chemical oxidative polymerization of aniline (ANI) with ammonium peroxydisulfate, in the presence of colloidal TiO2 nanoparticles (TiO2 NPs) (d ∼ 4.5 nm). Initial [TiO2]/[ANI] mole ratios were 20, 50, and 80. In the second step, following the polymerization process, the carbonization of PANI/TiO2 nanocomposites was performed by thermal treatment in an inert atmosphere at 650 °C. The morphological and structural properties of the carbonized nanocomposites were studied using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and Raman spectroscopy. The accomplishment of complete carbonization of PANI in PANI/TiO2 nanocomposites was confirmed by Raman spectroscopy. The appearance of anatase and rutile crystal forms in TiO2 NPs upon carbonization, with mass ratio depending on the initial molar ratio of ANI and TiO2 NPs was revealed by XRD measurements, TEM, SEM and Raman spectroscopy. The photocatalytic activities of carbonized PANI/TiO2 nanocomposites were evaluated following the photocatalytic degradation processes of Rhodamine B and Methylene blue. Carbonized PANI/TiO2 nanocomposites showed higher photocatalytic efficacy compared to bare TiO2 NPs and non-carbonized PANI/TiO2 nanocomposites. The porosity and surface structure of carbonized PANI/TiO2 nanocomposites, as well as crystalline structure of TiO2, affect photocatalytic activity of nanocomposites.
Keywords: Photocatalysis; TiO2; Carbonized polyaniline;
Support effects of NiW catalysts for highly selective sulfur removal from light hydrocarbons by J.N. Díaz de León; L.A. Zavala-Sánchez; V.A. Suárez-Toriello; G. Alonso-Núñez; T.A. Zepeda; R.I. Yocupicio; J.A. de los Reyes; S. Fuentes (167-176).
Display OmittedThe intrinsic support effect was explored in the preparation of NiW hydrodesulfurization catalysts through building correlations of catalytic performance to extensive surface characterization results. We found that the catalytic activity on the hydrodesulfurization of 3,methyl-thiophene correlates well with the normalized intensities data of NO adsorbed on Ni active sites. Also, a correlation between the catalytic activity and the number of tungsten edge atoms in the WS2 slabs was observed. The characterization of the NiW catalysts revealed that is possible to modulate the metal-support interaction by substituting the carrier. This specific interaction with each support derived into particular morphological parameters for the sulfide active phase. Optimal values for the slab length and the stacking of the WS2 slabs were proposed.
Keywords: Hydrotreatment; Hydrodesulfurization; Support effect; Supported catalysts; Sulfur removal; NiWS;
In-operando elucidation of bimetallic CoNi nanoparticles during high-temperature CH4/CO2 reaction by Bedour AlSabban; Laura Falivene; Sergey M. Kozlov; Antonio Aguilar-Tapia; Samy Ould-Chikh; Jean-Louis Hazemann; Luigi Cavallo; Jean-Marie Basset; Kazuhiro Takanabe (177-189).
Display OmittedDry reforming of methane (DRM) proceeds via CH4 decomposition to leave surface carbon species, followed by their removal with CO2-derived species. Reactivity tuning for stoichiometric CH4/CO2 reactants was attempted by alloying the non-noble metals Co and Ni, which have high affinity with CO2 and high activity for CH4 decomposition, respectively. This study was focused on providing evidence of the capturing surface coverage of the reactive intermediates and the associated structural changes of the metals during DRM at high temperature using in-operando X-ray absorption spectroscopy (XAS). On the Co catalysts, the first-order effects with respect to CH4 pressure and negative-order effects with respect to CO2 pressure on the DRM rate are consistent with the competitive adsorption of the surface oxygen species on the same sites as the CH4 decomposition reaction. The Ni surface provides comparatively higher rates of CH4 decomposition and the resultant DRM than the Co catalyst but leaves some deposited carbon on the catalyst surface. In contrast, the bimetallic CoNi catalyst exhibits reactivity towards the DRM but with kinetic orders resembling Co catalyst, producing negligible carbon deposition by balancing CH4 and CO2 activation. The in-operando X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements confirmed that the Co catalyst was progressively oxidized from the surface to the bulk with reaction time, whereas CoNi and Ni remained relatively reduced during DRM. Density functional theory (DFT) calculation considering the high reaction temperature for DRM confirmed the unselective site arrangement between Co and Ni atoms in both the surface and bulk of the alloy nanoparticle (NP). The calculated heat of oxygen chemisorption became more exothermic in the order of Ni, CoNi, Co, consistent with the catalytic behavior. The comprehensive experimental and theoretical evidence provided herein clearly suggests improvement to the catalyst design protocol by selecting the appropriate composition of Co-Ni alloy.
Keywords: Dry reforming of methane; Nickel; Cobalt; Bimetal; Carbon deposition; Kinetics; Density functional theory; In-operando X-ray absorption spectroscopy;
Removal of pendimethalin from soil washing effluents using electrolytic and electro-irradiated technologies based on diamond anodes by Perla T. Almazán-Sánchez; Salvador Cotillas; Cristina Sáez; Marcos J. Solache-Ríos; Verónica Martínez-Miranda; Pablo Cañizares; Ivonne Linares-Hernández; Manuel A. Rodrigo (190-197).
Display OmittedThis work describes the treatment of soil polluted with the herbicide pendimethalin by the combination of surfactant-aided soil-washing (SASW) and electrochemical advanced oxidation processes. Results show that it is possible to completely extract the herbicide from soil using SDS (sodium dodecyl sulfate) solutions as soil washing fluid (SWF) and ratios SWF/soil higher than 10 dm3 kg−1. Soil washing effluents obtained after the application of the SASW consisted of a mixture of surfactant (high concentration) and pesticide (low concentration) and their degradation by electrolysis, photo-assisted electrolysis (photoelectrolysis) and sonoelectrolysis with diamond anodes has been compared with that obtained by the application of single photolysis and sonolysis. Opposite to photolysis and sonolysis, the different electrolytic techniques allow decreasing the concentration of herbicide and surfactant in the effluents. Competition between the surfactant and the herbicide oxidation is important and irradiation of high-frequency ultrasound or UV light do not seem to outperform very importantly the results obtained by single electrolysis in the effluents of the SASW obtained with low SDS/soil ratios. Opposite, photoelectrolysis becomes the most efficient technology for the treatment of SWF obtained at high SDS/soil ratios (those required for an efficient SASW). Catalytic effect of the sulfate released during the degradation of SDS (in particular the formation of sulfate radicals) can help to explain the differences observed. The removal efficiency is higher during sonoelectrolysis, reaching a final removal of the pesticide after 8 h of treatment of 86.22%. Photoelectrolysis (57.59%) shows higher efficiencies for the removal of SDS followed by sonoelectrolysis (52.64%) and, finally, electrolysis (48.29%), after 8 h of treatment.
Keywords: Surfactant-aided soil washing; Electrolysis; Pendimethalin; Diamond anodes; Photoelectrolysis; Sonoelectrolysis;
Key factors in Sr-doped LaBO3 (B = Co or Mn) perovskites for NO oxidation in efficient diesel exhaust purification by Jon A. Onrubia; B. Pereda-Ayo; U. De-La-Torre; Juan R. González-Velasco (198-210).
Display OmittedPerovskites have attracted attention in recent years as an economic alternative to noble metals in oxidation processes. Synthesis conditions of LaCoO3 and LaMnO3 perovskites have been studied varying citrate to nitrate molar ratio in the starting solution, pH and calcination protocol, with the aim of obtaining high purity perovskites, absence of impurities, and with enhanced textural properties. Once synthesis conditions were established, strontium was incorporated in the perovskite lattice as a textural and structural promoter, by substituting lanthanum with different doping levels, i.e. La0.9Sr0.1BO3, La0.8Sr0.2BO3, La0.7Sr0.3BO3, La0.6Sr0.4BO3 and La0.5Sr0.5BO3 with B = Co or Mn. The prepared solids were characterized in terms of crystalline phase identification (XRD), specific surface area (N2 adsorption–desorption at −196 °C), reducibility and oxidation state of transition metal ions (H2-TPR), quantification of adsorbed oxygen species (O2-TPD) and surface elemental composition (XPS). Charge imbalance associated to strontium (Sr2+) incorporation in the perovskite lattice in substitution of lanthanum (La3+) was preferentially balanced by Mn4+ promotion in La1−x Sr x MnO3 perovskites, whereas formation of oxygen vacancies seems to be the mechanism for charge compensation in La1−x Sr x CoO3 perovskites, where Co ions remained as Co3+ ions. Strontium doped perovskites further improved NO conversion compared to the non-substituted formulations. The best NO oxidation performance was obtained with La0.7Sr0.3CoO3 and La0.9Sr0.1MnO3 samples, achieving maximum NO conversion of 83 and 65% at 300 and 325 °C, respectively. Higher oxidation capacity of La0.7Sr0.3CoO3 sample was associated to the higher oxygen mobility and exchange capacity between oxygen in the lattice and gas phase oxygen. It is worth noting that prepared perovskites presented far higher NO oxidation capacity than platinum-based NSR model catalysts, confirming perovskites as an economic alternative to catalyze NO oxidation reactions in automotive catalysis.
Keywords: Perovskite; LaCoO3; LaMnO3; Sr-doping; Surface oxygen vacancies; NO oxidation; Pt-free catalyst;
Highly active and selective Au thin layer on Cu polycrystalline surface prepared by galvanic displacement for the electrochemical reduction of CO2 to CO by Jun-Hyuk Kim; Hyunje Woo; Su-Won Yun; Hyun-Woo Jung; Seoin Back; Yousung Jung; Yong-Tae Kim (211-215).
Display OmittedAn electrochemical reduction of CO2 to CO has become a challenging issue in CO2 utilization in order to mitigate the climate change. In this study, we report a promising approach to prepare Au-based electrocatalysts for the electrochemical reduction of CO2 to CO having the maximized activity/selectivity and the minimized Au usage. It was clearly confirmed that the Au thin layer formed by the electrochemical galvanic displacement on polycrystalline Cu surface resulted in a markedly enhanced performance for the electrochemical reduction of CO2 to CO. The CO Faradaic efficiency for the Au thin layer on Cu was 10.6 and 3.4 times higher than that for the polycrystalline Cu and Au, respectively. It was revealed from the photoemission spectroscopy (PES) studies that the increase of electron population in s-band and the upshift of d-band center position of Au in Au/Cu increased the bond strength with reaction intermediates leading to the enhancement of activity and the selectivity. Along with the electronic effect, the geometric effect like the increased the electrochemical surface area (ECSA) and proportion of low coordinated sites also played a substantial role in the performance enhancement.
Keywords: CO2 reduction; Au thin layer on Cu; Electronic structure; Charge transfer; D-band center; CO selectivity;